The global supply of renewable energy is rapidly increasing due to increases in generating facilities, such as those from wind and solar. The inherent instability of renewable energy sources, however, currently places a practical restriction such that only a maximum of 15-20% of a grid's power is projected to be derived from these sources. This limitation could potentially be alleviated or even eliminated by integrating electrical energy storage (EES) technologies into the grid. Electrical energy storage technologies are highly desired for both their environmental and economic benefits, as EES would allow increased utilization of existing power plants in addition to introducing possibilities of energy arbitrage.
Of the existing EES technologies, pumped hydro storage has the largest installed storage capacity globally, estimated at over 130 gigawatts. Geographical (limited number of candidate sites) and ecological (concerns with dams causing habitat destruction) considerations will likely limit future development of pumped hydro storage. The only other grid energy storage technology with similar performance to pumped hydro storage is compressed air energy storage (CAES). CAES was originally developed in the early 1960s and stores energy in the elastic potential energy of compressed air. With the demand for energy storage technologies following the rapid increase in deployment of renewable energy sources, there has been renewed interest in CAES. However, a significant technical issue with CAES is that when the air is compressed approximately half of the exergy created is in the form of heat. This heat energy is energy that can be lost if not properly stored.
To reduce the heat loss, different proposals have been advanced in the literature which propose to store thermal energy using various heat storage materials. This concept of storing thermal energy in a heat storage material is known as adiabatic compressed air energy storage. Literature reports have concluded phase change materials (PCMs) are not a viable candidate for use as a thermal energy storage material for compressed air energy storage systems based on assessments that “no single (PCM) system can cover the (large temperature) range” required by such a system. See, e.g., Bullough et al., “Advanced Adiabatic Compressed Air Energy Storage for the Integration of Wind Energy,” Conference Advanced Adiabatic Compressed Air Energy Storage for the Integration of Wind Energy, London, UK (2004).